Abstract:
Maize (Zea mays L.), a key staple crop in Sub-Saharan Africa, is particularly
vulnerable to concurrent drought and heat stress, which threatens crop yield and
food security. Plant growth-promoting rhizobacteria (PGPR) have shown
potential as biofertilizers to enhance plant resilience under such abiotic
stresses. This study aimed to (1) identify PGPR isolates tolerant to drought and
heat, (2) assess their capacity to mitigate the effects of these stresses on early
maize growth, and (3) analyze maize gene expression changes associated with
PGPR-induced tolerance. Rhizobacteria were isolated and screened for drought
and heat tolerance, alongside key plant growth-promoting (PGP) traits, including
phosphorus solubilization, nitrogen fixation, and indole acetic acid production. In
vitro and pot trials evaluated the effects of selected isolates on maize growth
under stress, using indicators such as shoot length, root and shoot biomass (wet
and dry), and leaf water content. Quantitative reverse transcription PCR (qRTPCR) was employed to profile maize stress response genes. The identified PGPR
isolates included Bacillus cereus (11MN1), Bacillus pseudomycoides (21MN1B),
Lelliottia amnigena (33MP1), and Leclercia adecarboxylata (36MP8). Greenhouse
trials demonstrated that L. amnigena 33MP1, L. adecarboxylata 36MP8, and a
mixed culture of isolates (11MN1, 21MN1B, 33MP1, 36MP8) effectively alleviated
the adverse effects of concurrent drought and heat stress in maize. Notably, qRTPCR analysis indicated that PGPR-induced tolerance may involve the modulation of stress response genes CAT2 (catalase 2) and DHN2 (dehydrin 2), which play
roles in oxidative stress management and cellular protection. The PGPR isolates
identified in this study represent promising bioinoculants for enhancing maize
resilience under climate-induced stresses, offering a sustainable approach to
improve maize productivity, conserve water, and reduce irrigation needs in
drought-prone regions.
